How to Rack a Kel-Tec P3AT Slide
(or any other slide that's stiffly sprung)

Grasp pistol's grip in strong hand, as if to shoot.

Grasp slide at serrations with weak hand, using thumb and as many fingers as possible.

Brace weak-side arm tightly against body and don't move it.

Sharply push pistol away from you with strong hand.

If That Doesn't Work, Try This:

Grasp pistol's grip in strong hand, as if to shoot.

Grasp slide at serrations with weak hand, but with hand reversed (thumb towards body). Hold slide between all fingers and pad of heel of hand (including thumb). It's OK if the pistol's ejection port is covered by your hand.